Internally viewable microwave induction heater

ABSTRACT

The present invention relates to an internally viewable microwave induction heater comprised of conductive screen, the width and height of whose meshes are small compared to the wavelength of selected microwaves within said internally viewable microwave induction heater. The selected microwaves do not pass through said meshes but remain contained within the interior of said internally viewable microwave induction heater. A microwave susceptible material within said internally viewable microwave induction heater can be visually observed while it is being inductively heated.

United States Patent [72] Inventor 2 1 Appl. No. 875,195

[22] Filed [45] Patented Nov. 10, 1969 July 20, 1911 [54] INTERNALLY VIEWABLE MICROWAVE Primary Examiner-J. V. Truhe Assistant ExaminerL. H. Bender Attorney-John P. Tarlano INDUCTION HEATER 6 Claims, 4 Drawing Figs.

52 u.s.c1 219 1055,

219/ 143, 219/10-49 ABSTRACT: The present invention relates to an internally Int. viewable microwave induction heater comprised of cgnduc- 5/00 tive screen, the width and height of whose meshes are small of Search compared to the wavelength of selected microwaves 10-43, 10-49 said internally viewable microwave induction heater. The 56 R i cud selected microwaves do not pass through said meshes but I l e erenm I remain contained within the interior of said internally viewa- UNITED STATES PATENTS ble microwave induction heater. A microwave susceptible 2,747,066 5/1956 Brace 219/10.43 material within said internally viewable microwave induction 2,956,144 10/1960 Woodman 219/ 10.55 heater can be visually observed while it is being inductively 2,993,973 7/1961 Johnson et a1. 219/ 10.55 heated.

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su PPkY 15 l7 i 21 I? Ef ans SUPPLY PATENTEU JUL20 m1 SHEET 1 OF 2 INVENTOR RALPH L. HOUGH ms ATTORNEY PATEN TEflJuLaomn sum 2 or 2 OXYGEN aqppul mvsmon I RALPH L HOUGH BY Has ms ATTORNEY INTERNALLY VIEWABLE mcnowxvs INDUCTION HEATER BACKGROUND OF THE INVENTION In the prior art is disclosed a microwave cavity which is composed of a solid material which does not have closely spaced meshes therein. Such a microwave cavity is not internally viewable and easy to fabricate. Such a microwave cavity has not been used very successfully as an induction heater due to its opaqueness,,difficulty to fabricate, and difficulty of operation. The internally viewable microwave induction heater of the present invention is easily fabricated, internally viewable, and amenable of various easily designed configurations. The internally viewable cavity is fabricated from conductive screen, the width and height of whose meshes is small compared to the wavelength of selected microwaves within said internally viewable microwave induction heater. A microwave source is connected to the internally viewable microwave induction heater to allow selected microwaves to inductively heat a susceptor therein. I

SUMMARY OF THE INVENTION closed, conductive screen having a microwave entrance therein, for accepting and holding microwaves within the interior of said three-dimensionally closed, conductive screen, the width and length of the meshes of the conductive screen being less than one-thirtieth of the wavelength of the selected microwaves to be within the interior of said three-dimensionally closed, conductive screen.

Accordingly, it is an object of the present invention to provide a new microwave induction heater furnace system which is capable of achieving very high specimen temperatures.

Yet another object of the present invention is to provide a new microwave induction heater which is amenable to economy of fabrication,

Still another object of the present invention is to provide a microwave induction heater which is easily placed around a desired processing space, and which may be removed with equal ease.

Still another object of the present invention is to provide a microwave induction heater which permits visibility of a specimen during its heating.

DESCRIPTION OF THE DRAWINGS FIG. I is a plan view of a double-conically shaped internally viewable microwave induction heater furnace system.

FIG. 2 is a perspective view of a cylindrically shaped internally viewable microwave induction heater furnace system.

FIG. 3 is a perspective view of a rectangularly shaped internally viewable microwave induction heater furnace system for heating food.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. la, a waveguide 10, with flanges 12 therein, is connected to a 26.5-inch long double-conically shaped internally viewable microwave induction heater 14. The internally viewable microwave cavity 14 is. comprised of conductive screen 16, which has l-mm. wide square meshes l7, spaced 0.l-mm. apart by 0.1-mm. copper wire. The internally viewable double-conically shaped microwave cavity 14 is made semirigid by supporting each 12-inch long copper screen cone 24 by means of a 2.5-inch long and 4-inch in diameter brass cylinder 18. The brass cylinder 18 has a microwave window looking into the waveguide and of the same dimensions as the waveguide. Load matching is conveniently accomplished by inductive shunts, sidewall hybrid junctions, or other conventional tuning methods well known to the art. Each conductive screen cone 24 of the internally viewable microwave induction heater 14 ends in a 2-inch long and 0.25-inch internal diameter hollow copper tip 20. A quartz furnace tube 22 passes through the hollow copper tips of the internally viewable microwave cavity 14.

power supply 23 into klystron 21, is maintained at approxi mately 50 watts.

The microwaves, which have a wavelength of nominally 120 mm., enter into the internally viewable microwave cavity 14 through microwave window 19 and do not escape through meshes 17. The microwaves remain in the internally viewable microwave cavity 14 to inductively heat a 0.00l-inch diameter carbon filament 28 within said quartz furnace tube 22 with radiant energy. The quartz tube 22 does not reach a temperature of over 400 C., but the carbon filament 28 is inductively raised to a temperature of 2,000 C. No appreciable amount of microwave energy is absorbed by the quartz furnace tube 22 since the quartz furnace tube is not susceptible, and it is not in the region of maximum field within the cavity. The carbon filament 28 is susceptible and is also located in the focused energy of the microwave field. Noapprec'iable microwave energy is absorbed by the conductive screen 16 of the internally viewable microwave cavity 14, which remains near room temperature, due to the high electrical conductivity of the copper screen 16. However, energy is absorbed by a conductive filament such as carbon filament 28.

Ethyl iodide doped ethylene 29 from gas supply 27 is passed through the quartz furnace tube at ZOO-ml. per minute. During the inductive heating of the carbon filament 28 to 2,000c., one may observe its being coated with more carbon through the meshes 17 within the internally viewable microwave cavity I4 due to the decomposition of ethylene 29 at the site of the hot carbon filament 28. After 5 minutes of processing, the carbon filament 28 has a large tensile strength of 140,000 p.s.i. due to it being coated with additional carbon.

When a poor conductor such as carbon is placed within the quartz furnace tube 22, microwaves entering into the internally viewable microwave inductive heater 14 will be absorbed by said conductor so as to inductively heat said conductor. The conductor, such as a carbon filament, may be inductively heated to a temperature of over 2000 c. by means of the internally viewable microwave induction heater of the present invention. Such an internally viewable microwave induction heater 14 may be used to grow quartz whiskers on a 0.002-inch diameter tungsten wire by passing vapors of ethyl-o-silicate gas through the quartz furnace tube 22 for 10 minutes. The inductively heated tungsten wire in the quartz furnace tube 22 may be visually inspected during the growing process within the internally viewable microwave induction heater 14. That is, a single-crystalline material may be grown within quartz furnace tube 22.

The preferred embodiment of FIG. la may be extended for utilization in chemical processing of gaseous or liquid streams. Thus, the tube may be extended lengthwise to become a conduit in a processing assembly. A stream of gas or liquid confined therein and flowing axially is subject to the influence of the microwave field confined to the volume bounded by the screened surfaces. Viewpoints along the conduit are so arranged that the reaction site is observable through the screened surfaces. The conic screens may also be inverted as shown in FIG. lb to increase the high-voltage component of the microwave field to enhance ionization and other plasma effects which are used to advantage in the conversion of 0 and 0 and for other chemical processing.

FIG. 2 shows a cylindrically shaped internally viewable microwave induction heater 30 comprised of conductive screen having l-mm. wide square meshes 33. The internally viewable microwave induction heater 30 is built upon a quartz tube '32. The cylindrically shaped internally viewable microwave induction heater 30 from a klystron 43 so as to heat the silicon semiconductor'4l to a temperature of approximately"l,l C. Oxygen gas 47 from oxygen supply 46 is passed through the quartz furnace tube 32 at l-liter per minute. The oxygen gas 47 passes out of said quartz furnace tube 32 through valve 48. One can visually observe the growing of a silicon dioxide layer 45 upon the silicon semiconductor wafer 41' within the cylindrically shaped microwave induction heater 30.

FIG. 3 shows a parallelepiped shaped internally viewable microwave induction heater 60. The microwave induction heater 60 is comprised of conductive screen 61 having l-mm. wide and l-mni'. high meshes 63. The microwave induction heater has hinges 62 thereon, which support a conductive screen port 64, so as to allow access to the interior of said internally viewable microwave induction heater 60. A specimen 70 to be heated, such as food, can be placed within the interior of said internally viewable microwave induction heater 60. The food 70 is heated in the microwave induction heater 60 by interaction of the food 70 and the microwave field.

lelaim:

1. An internally viewable microwave induction heater comprising: a three-dimensionally closed, meshed conductive wire screen having a microwave entrance therein, for accepting and'holding elected microwaves within the interior of said three-dimensionally closed, meshed conductive wire screen, the width and length of the meshes of the meshed conductive wire screen being less than one-thirtieth of the wavelength of the selected microwaves to be held within the interior of said three-dimensionally closed, meshed conductive wire screen, the thickness of the wire of the meshed conductive wire screen being approximately 0.l mm..

2. An internally viewable microwave induction heater system, comprising:

a. A source means for supplying microwaves of a selected wave length; b. Waveguide means connected to said source means for transferring microwaves; and v c. A three-dimensionally closed meshed conductive wire screen, microwave cavity the width and length of whose meshes are small compared to the wavelength of the selected microwaves, connected to said waveguide means to allow microwaves to enter from said waveguide means and remain therein, the thickness of the wire of the meshed conductive wire screen being approximately 0.1

3. An internally viewable microwave induction heater system comprising:

a. A source means for supplying microwaves of a selected wavelength;

b. Waveguide means connected to'said source means for transferring microwaves;

c. A three-dimensionally closed meshed conductive wire screen, microwave cavity the width and length of whose meshes are small compared to the wavelength of the selected microwaves, connected to said waveguide means to allow microwaves to enter from said waveguide means and remain therein, the thickness of the wire of the meshed conductive wire screen being approximately 0.1 mm.; and

d. Susceptor means for holding a specimen thereon within said internally viewable microwave cavity, the susceptor means to be inductively heated by microwaves within said internally viewable microwave |nduction heater in order to heat the specimen on the inductively heated susceptor means.

4. The internally viewable microwave induction heater system of claim 3 wherein the three-dimensionally closed meshed conductive wire screen, microwave cavity is a doubleconically shaped meshed conductive wire screen microwave cavity.

5. The internally viewable microwave induction heater system of claim 3 wherein the three-dimensionally closed meshed conductive wire screen, microwave cavity is a cylindrically shaped meshed conductive wire screen, microwave cavity.

6. The internally viewable microwave induction heater system of claim 3 wherein the three-dimensionally closed, meshed conductive wire screen, microwave cavity are conic surfaces held to the interior of a long tubular conduit and so arranged with vertices opposed or adjacent as to provide microwave field voltage components suitable for producting chemical or physical effects upon a process steam flowing axially therein. 

1. An internally viewable microwave induction heater comprising: a three-dimensionally closed, meshed conductive wire screen having a microwave entrance therein, for accepting and holding elected microwaves within the interior of said threedimensionally closed, meshed conductive wire screen, the width and length of the meshes of the meshed conductive wire screen being less than one-thirtieth of the wavelength of the selected microwaves to be held within the interior of said threedimensionally closed, meshed conductive wire screen, the thickness of the wire of the meshed conductive wire screen being approximately 0.1 mm..
 2. An internally viewable microwave induction heater system, comprising: a. A source means for supplying microwaves of a selected wave length; b. Waveguide means connected to said source means for transferring microwaves; and c. A three-dimensionally closed meshed conductive wire screen, microwave cavity the width and length of whose meshes are small compared to the wavelength of the selected microwaves, connected to said waveguide means to allow microwaves to enter from said waveguide means and remain therein, the thicknesS of the wire of the meshed conductive wire screen being approximately 0.1 mm..
 3. An internally viewable microwave induction heater system comprising: a. A source means for supplying microwaves of a selected wavelength; b. Waveguide means connected to said source means for transferring microwaves; c. A three-dimensionally closed meshed conductive wire screen, microwave cavity the width and length of whose meshes are small compared to the wavelength of the selected microwaves, connected to said waveguide means to allow microwaves to enter from said waveguide means and remain therein, the thickness of the wire of the meshed conductive wire screen being approximately 0.1 mm.; and d. Susceptor means for holding a specimen thereon within said internally viewable microwave cavity, the susceptor means to be inductively heated by microwaves within said internally viewable microwave induction heater in order to heat the specimen on the inductively heated susceptor means.
 4. The internally viewable microwave induction heater system of claim 3 wherein the three-dimensionally closed meshed conductive wire screen, microwave cavity is a double-conically shaped meshed conductive wire screen microwave cavity.
 5. The internally viewable microwave induction heater system of claim 3 wherein the three-dimensionally closed meshed conductive wire screen, microwave cavity is a cylindrically shaped meshed conductive wire screen, microwave cavity.
 6. The internally viewable microwave induction heater system of claim 3 wherein the three-dimensionally closed, meshed conductive wire screen, microwave cavity are conic surfaces held to the interior of a long tubular conduit and so arranged with vertices opposed or adjacent as to provide microwave field voltage components suitable for producting chemical or physical effects upon a process steam flowing axially therein. 